It is known to provide electrical machines which comprise a stator assembly formed from laminations of appropriate material in order to create poles which magnetically interengage with a rotor. The electrical machine constitutes a motor driven by magnetic engagement between the stator assembly and the rotor. Typically, the stator is appropriately constructed in order to comprise a succession of electromagnets whose pole characteristics can be alternated in order to drive the rotor, which in this case incorporates permanent magnets.
The stator assembly typically comprises a number of C shaped stator cores assembled in a circular hub with the rotor passing through the open jaw of each C shaped stator core. Typically, the C shaped cores are manufactured by winding a strip of grain oriented electrical steel around a former and then impregnating with an adhesive and curing. The open jaw is subsequently created by machining in order to make the correct shape of material in the region of the tips (also known as stator poles).
It will be understood that it is the tips of these jaws which transmit the rotational torque forces to the stator and also experience jaw closing forces due to the magnets in the rotor. In operation, these forces are cyclical, but the closing force component is also present when the machine is stationary. Thus, the tips tend to move in operation and the whole C core is subject to vibration and can generate excessive audible noise. The vibration can also cause delaminations of the wound lamination material in the region of the tips. The individual laminations lack strength and can be pulled into contact with the rotor by the magnetic forces. Also, even when stationary, the C cores as a whole experience the closing force which over time causes creepage of the bonding adhesive leading to closure of the tips onto the rotor even if vibration induced delamination has not occurred.